Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus.
In terms of architecture, the terminal end of a cased well often extends into an open-hole lateral leg section. In many cases, multiple leg sections of this nature extend from a single main vertical well bore. Such architecture may enhance access to the reservoir, for example, where the reservoir is substantially compartmentalized. Regardless, such open-hole lateral leg sections often present their own particular challenges when it comes to their completions and maintenance.
In terms of completions, a variety of hardware may be installed before the well and various legs are ready for production operations. That is, in addition to the noted casing, hardware supporting various zonal isolations or chemical injection lines may be installed. Additionally, perforating, fracturing, gravel packing and a host of other applications may be employed in completing the well and various leg sections.
With particular reference to the lateral legs and other open-hole regions, the noted gravel packing and other production related enhancements may rely on the presence of a formation isolation valve. That is, such a valve may be disposed at the interface of cased and open-hole well regions so as to ensure a separation between completion and production fluids. More specifically, comparatively heavier fluids utilized during completions may be prone to adversely affect the formation if allowed to freely flow to the production region. By the same token, production of lighter high pressure fluids into the main bore during hardware installations may adversely affect such operations. Therefore, formation isolation valves may be disposed in cased regions of the well near the interface of open-hole well regions.
Each lateral leg may be outfitted with a formation isolation valve that may be opened for gravel packing and other early stage leg applications. However, such valves may be subsequently closed to isolate the open-hole portion of the leg as other completions are carried out elsewhere in the well.
As indicated, closing the valve may avoid fluid loss during completions operations and also maintain well control in the sense of avoiding premature production of well fluids. This closure may be achieved in conjunction with removal of application tools from the open-hole region of the leg. So, for example, following a gravel packing application in a lateral leg, a shifting device incorporated into the gravel packing wash pipe may be used to close off the valve as the assembly is removed from the area. Thus, completion of the application and retrieval of the tool involved may be sufficient to close the formation isolation valve.
Unfortunately, once the well is completed and ready for production, re-opening the valve may be a bit more challenging. For example, a shifting tool may be re-introduced into the well and directed at each valve, one by one. Of course, depending on the depth and sophistication of the well architecture, this may eat up one to three days of time as well as a significant amount of footspace at the oilfield. Further, equipment costs in terms of up-rigging may also be incurred. For example, where the legs at issue are of a horizontal nature, coiled tubing operations may be required for delivery of the shifting tool. Once more, the interventional nature of shifting tool delivery inherently involves the possibility of mechanical failure and/or potential damage to the tool itself, particularly when considering the sudden emergence of high pressure conditions as each valve is sequentially opened.
In order to address the potentially costly drawbacks associated with interventional shifting tool delivery to re-open the valves, wireless, pressure based opening techniques have been developed. For example, each leg of the multilateral may be outfitted with a formation isolation valve that incorporates a pressure responsive actuator for opening the valve. Thus, sufficient pressure may be introduced into the well from the surface of the oilfield in order to trigger the actuators to open their respective valves and allow production to commence.
Unfortunately, in the described scenario, the actuators may not all open at precisely the same time. For example, the pressure increase may propagate unevenly or one actuator may be responsive to a slightly different pressure than another. When this occurs, the responsive actuators and associated open valves serve as an impediment to pressure actuation for any remaining un-open valves. That is, once one of the valves has been opened, continued efforts to pressure up the well and trigger other actuators are likely to only result in dumping fluid into the newly open-hole lateral leg. As a result, operators are then left with the only practical option being to resort to mechanical intervention in the form of a costly shifting tool application as noted above.